Engines which utilize combustion at constant volume rather than constant pressure so that the additional kinetic efficiency of constant volume combustion can be utilized have been known heretofore. Early examples include such engines as the pulsed jet used in the German buzz bombs and the explosion combustion engines of Holzwarth. Other examples include the use of movable valves in back of the compressor and in front of the turbine. Still other examples include the use of stationary combustion chambers symmetrically spaced over the circumference of the engine with a rotary ignition sequence, such as shown in U.S. Pat. 3,877,219 issued Apr. 15, 1975.
In addition, various systems have been proposed to try to improve the combustion efficiency of conventional Brayton cycle gas turbine engines. Increasing the air velocity within the combustion chamber has been tried so that the velocity difference develops more kinetic energy. However, combustion instability and flame-out can occur because of Rayleigh line flow conditions. Thus, a choked flow condition will be reached before an increase in stagnation pressure will occur.
Intermittent choking has been tried by rapid-pulsing the after burner. Only small pressure increases can be achieved, however, before combustion instability or turbine blade damage occur along with non-isentropic flow conditions and shock wave dissipation of energy.
All of the previous proposed engines have not yielded the full kinetic potential of constant volume combustion. These devices use valves, gates, vanes or choked flow conditions which induce intermittent or pulsed flow conditions. The result is reduced air flow volume through the engine producing non-isentropic flow conditions with kinetic energy losses. In addition, combustion instability and incomplete combustion result from the ignition of a stratified charge in an unsteady flow condition.